Rock or Mineral?

We're going to start this lesson on rocks and minerals by talking about chemistry, not geology. You'll understand why in just a minute. Chemistry - what is it? According to Merriam-Webster, chemistry is:

"A science that deals with the composition, structure, and properties of substances and with the transformations they undergo."

In short, chemistry is the study of substances - elements and compounds and all the reactions that happen between them. Did you notice that we highlighted the word 'elements'? Elements are the key to understanding rocks and minerals, so let's take a few minutes to understand what elements are.

Elements are the simplest, most basic type of a chemical substance. Elements cannot be broken down into other substances by chemical reactions. They are made of a basic, incredibly small particle called an atom, which contains protons and neutrons inside it's nucleus with electrons surrounding it in a fuzzy orbit. (Don't worry - we won't be going into too much detail, but we want to set the stage for mineral formation, so stick with us on this.) To the right is a visualization of a basic atom with its parts.

Every atom has a set number of protons inside its nucleus. The number of protons inside the atom's nucleus determines its elemental identity, or which element it is. No two elements have the same number of protons in their atoms which means that every single element is unique. What's even better is that it's so easy to find out how many protons are in the nucleus of every single element. How is it so easy? The periodic table of elements! It's like a built-in cheat sheet but shhh...don't tell your teacher.

Notice that each element on the periodic table has a number. That number tells us how many protons the element has in its nucleus and is called the element's atomic number. Notice that every number, and therefore every element, is unique.

Let's work through one example element on the periodic table to determine some of its properties. Our example element will be magnesium. See if you can find it on the table above - it's atomic number is 12. Now that you've found element number 12, you should also see that it's symbol is Mg. All elements are displayed as symbols and most have symbols that are similar to their names (magnesium = Mg, lithium = Li) but there are others that aren't as easy to match (sodium = Na, gold = Au).

Why is magnesium number 12 on the period table? Because it has 12 protons in its nucleus. No other element has 12 protons and this number of protons is what gives magnesium its unique chemical properties. The number beneath the Mg symbol (24.305) is magnesium's atomic weight, a property which is beyond the scope of this lesson, so we're going to ignore that number for now.

Can you find the element zinc (Zn) on the table? What atomic number is it? What does that mean about the number of protons in its nucleus?

There are currently 118 elements on the periodic table and the number keeps growing. Many of the elements on the table occur naturally but there are quite a few that have been created by humans in a laboratory. The most recent additions were four new elements added in 2016. You can watch the video below to learn a bit more about how new elements are made and how they get added to the period table.

We've answered the very basic question of what elements are. Let's take this a step further and ask the question - do elements ever partner up with each other or bond with each other? The answer is a resounding YES, yes they do. Elements sometimes bond together in a crystalline structure to form.....wait for it.....MINERALS!

A few examples of elements bonding together to form minerals are:

• Sodium (Na) bonds with chlorine (Cl) to form NaCl (table salt) or the mineral halite
• Silicon (Si) bonds with oxygen (O) to form SiO ₂ , which is the mineral quartz
• Potassium (K) bonds with aluminum (Al), silicon (Si), and oxygen (O) to form the mineral potassium feldspar (see an image of this mineral in the next section "Mineral Basics")

Some elements are introverts and don't feel the need to bond with other elements to form minerals. Rather, they bond with other atoms of the same element. These are called native element minerals and a few examples are copper (Cu), gold (Au), and silver (Ag). They're elements but also minerals.

Yes, that's right. Minerals that are made of only one element are called native element minerals (gold, silver, copper, etc.) and minerals that are multiple elements bonded together are compounds. Easy as pie, right? It's now time to move on to a more in-depth look at minerals.

There are between 4,000 and 5,000 minerals known to exist on Earth. Each of those minerals are simply elements or compounds of elements but all must abide by some basic properties. To be a mineral, a substance must:

• Be inorganic (not made from once-living matter)
• Occur naturally (minerals made in laboratories or with elements made in laboratories are not true minerals)
• Be solid at room temperature (minerals cannot be liquid)
• Have a defined chemical composition (no other atoms or elements can be included in its structure)
• Have a regular crystalline structure (elements and compounds are arranged in a set pattern or arrangement)

There is some debate among geoscientists about ice. Is it a mineral? It meets every criteria in the list above except that it's not a solid at room temperature - ice melts into water at room temperature. We're going to stay out of this fray for now and let you decide!

One of the other basics of minerals is that each one has a unique set of physical properties. The elements and the arrangement of the elements or compounds determines those physical properties. By testing a specimen's physical properties, we can (hopefully) determine what mineral it is that we're looking at. Scroll through the images below to learn about some of the physical properties we can test.

With a few mineral samples and a few tools, you can test minerals just like geologists do!

We've learned what elements are. We've also learned that minerals are just one or more elements bonded together. So where, exactly, do rocks fit in to this? How are rocks and minerals related? Quite simply, rocks are made of one or more minerals.

There it is right there - the link between elements, minerals and rocks. Rocks are made from one or more minerals. Minerals, as we know, are made of one or more elements. It all fits together! This should clear up the age old question "Aren't rocks and minerals the same thing?" You can now answer this question with a definite NO! They're not the same but they are definitely related.

We've almost made it to the end of our story about the relationships between minerals and rocks but we haven't yet answered the basic question - is it a rock or a mineral? You've read this far so we can assume, at some point, you've found a cool sample and thought to yourself, "What kind of rock is this? Or is it a mineral"? The truth is, it's sometimes hard to tell the difference, even for geologists. Minerals often look like rocks and rocks often look like minerals. Below we'll provide a few observations you can make or tests you can do to determine if your sample is a rock or mineral, but before we do, there's one elephant in the room that we need to address.

We get a lot of inquires at the NC Geological Survey about rock samples and one of the most common questions we get asked is "Is this a meteorite?" Unfortunately, our answer is almost always "No, sorry, it's not a meteorite". Meteorite samples are highly uncommon - most meteors disintegrate in the atmosphere before reaching Earth's surface. If you're not convinced, there are a few tests and observations you can make at home and some great web resources to check out such as the University of Arizona's  Lunar and Planetary Laboratory , the  U.S. Geological Survey , and the  Utah Geological Survey .

• If your sample is a meteorite it will have a fusion crust - a paper-thin, dark brown or black crust on the surface. The meteor's surface melts during its journey through Earth's atmosphere and will leave a glassy skin on the outside.
• Is your sample quite heavy for its size? Meteorites contain iron and dense minerals so if it's a true meteorite, it will be hefty for its size.
• Use a magnet to test for magnetism in your sample. Since meteorites contain iron, a magnet should be attracted to your sample, especially if you hang the magnet on a string and pass it close by your sample.
• Run the sample across a streak plate. If it leaves a streak, it's not a meteorite.
• Does your sample have light colored minerals? If it does, it's not a meteorite.
• Does your sample have small holes or vesicles? If it does, it's not a meteorite.

Check out the resources we've noted in this section for more information on meteorites and their identification. Who knows - maybe you'll be that lucky, one-in-a-million person to find a meteorite!

Now let's get back to our regularly scheduled discussion on ways to identify your sample as a rock or mineral.

MINERAL TESTING: You could use the testing information provided earlier plus a few tools to test the sample, if you're fairly certain it's a mineral. You can easily test properties like hardness, streak, magnetism, and acid reaction. Based on the test results and a bit of internet research, you have a good shot of determining what mineral you have.

COLOR: Although mineral color can vary based on weathering or impurities, one rule of thumb is that most minerals tend to be one color. That's not a hard and fast rule, but most rocks are made from several minerals, which means the possibility of several colors.

TEXTURE: Texture means how the rock or mineral looks - its appearance, mineral crystal size, how the crystals are sorted, or even how large or small they are. One texture is called foliation, which is repeated layers of minerals, like pages in a book. There are a few minerals that show foliated texture:

There are some metamorphic rocks that can show foliated textures, as well. Keep in mind that foliated minerals tend to have minimal colors, whereas foliated metamorphic rocks will often have layers of at least two colors and often have some shiny mineral crystals.

If you have a sample that's foliated, you can narrow down the list of minerals or rocks that it can be.

If you still can't determine what your sample is, please take a look at the North Carolina Geological Survey's  statewide geologic map . You can search for the address of where your rock or mineral specimen was found (look for the little magnifying glass in the upper left corner). Once you find the rock or mineral type for that location, you can do a bit of online research to see what typical rocks or minerals of that kind look like. This map is a great tool to learn about all the rocks and minerals of North Carolina so take some time to explore more while you're there.

There are two ways that geologists here at the North Carolina Geological Survey can help you identify your mystery mineral or rock (well three, actually, if you count looking at our online geologic map). For either of the two options below, please submit an email to our Section Chief Dwain Veach at dwain.veach@deq.nc.gov first to let us know you have a specimen that you'd like us to identify. He'll direct you to do one of the following:

1. PHOTO: It's particularly difficult for a geologist to identify a rock or mineral based on photo but if you can't submit a sample to us, you can take several photos of your sample but you must include an object in the photo to show us the scale/size of the sample. You can place your foot next to it, or lay a pen or other object next to the sample so that we can see its size. Take at least one close photo so we can see the minerals.
2. SAMPLE: Staff at the North Carolina Geological Survey do provide rock and mineral identification, free of charge, for samples sent to our offices. Samples should be securely packaged with a note that includes the street address where the sample was found and what you would like us to identify. We do not provide assays or do any chemical analyses.

We hope you learned a bit about the differences between minerals and rocks but also about how they're related. It can be tricky, even for geologists, so don't get down if you're having trouble identifying your cool sample. We have trouble, too! If you have any more questions, please send Senior Geologist Amy Pitts an email at amy.pitts@deq.nc.gov. Our Education and Outreach program is available to visit your school or group to teach more about rocks and minerals.